The invention relates generally to composite batteries, especially batteries for electric vehicles, in which a multitude of battery cells are electrically interconnected. Specifically, the invention relates to monitoring and controlling individual battery cells within a composite battery comprising a multitude of battery cells by using analysis/control units on cell or block level for diagnosing and/or controlling the module's performance.
In electric vehicles, battery modules are a key enabler for driving performance and reliability. These battery modules are typically made up of a set of electrically interconnected battery cells, e.g., of to Li-ion type. In order to ensure efficient use of such battery modules, their components, particularly their cells, must be analyzed in detail and over time. Thus, the battery modules must be provided with diagnostic features which permit identification of under-performance or malfunction of battery cells within the modules without the need of disconnecting or disassembling them. These features should include anticipatory features which permit to assess not only the actual battery capacity, but also prospective behavior of the battery module.
Numerous battery monitoring systems exploiting a wide variety of battery parameters are known from the state of the art:
For example, U.S. Pat. No. 7,619,417 B2 describes a battery monitoring system which utilizes a minimum amount of input data (including voltage, current, temperature and conductance) to periodically determine vehicle battery status.
U.S. Pat. No. 7,576,545 B2 discloses systems and methods for predicting end of life of a Li-ion battery. Among others, a method is described which makes use of partially charging/discharging the battery, measuring an open circuit voltage of the battery before/after a partial charging/discharging and determining a state of charge value of the battery corresponding to the open circuit voltage measured before and after partial charging/discharging.
Further detection devices and methods for analyzing and monitoring the state of vehicle batteries are described in US 2009/0115419 A, US 2009/0027056 A1, US 2008/0048662 A1, U.S. Pat. No. 7,061,246 B2, U.S. Pat. No. 7,514,905 B2 and US 2009/0174369 A1. These methods are based on measurements of various battery parameters such as battery voltage, discharge current from the battery, internal resistance, etc. For example, US 2008/0048662 A1 suggests using the battery's impedance which may be obtained from measurements of voltage and current frequency components. U.S. Pat. No. 7,061,246 B2 describes a method for estimating battery lifetime by determining a representative parameter (which may be based, for example, on voltage and temperature) in a new, fully charged state and monitoring this parameter during use of the battery. U.S. Pat. No. 7,514,905 B2 and US 2009/0174369 A1 disclose battery management systems which use temperature, voltage and current to determine the battery state and enable optimum charge and discharge control. The temperature is measured in various locations within the battery, and respective values of maximum available charge/discharge powers or maximum available charge/discharge currents of the battery are determined for the minimum and maximum temperature.
A rechargeable battery with internal microcontroller is disclosed in US 2010/0039071 A1. This microcontroller stores data regarding the environment to which the battery is exposed and conveys these data to a charger used to charge the battery. If the data indicate that the battery may have been subjected to a harsh environment, the charger performs a full state of health evaluation of the battery.
US 2009/0210736 A1 discloses a computer system which gathers information relating to the operational state of a battery, calculates the health of the battery from the gathered information, provides the health and the operational state of the battery to a vehicle operator and includes means for supporting non-battery related functions.
U.S. Pat. No. 7,557,586 B1 describes an electronic battery tester for testing a battery pack comprising a plurality of batteries. The tester comprises a circuitry for measuring dynamic parameters of the battery pack, a memory for storing a multitude of known configurations (serial, parallel and series-parallel) of the batteries in the pack and a microprocessor for identifying the configuration and adjusting test criteria.
An on-line battery monitoring system for monitoring a plurality of battery cells is shown in U.S. Pat. No. 5,923,148 A. This system is capable of identifying and computing individual cell and battery bank parameters. The system comprises a controller for designating a given battery cell to be monitored, a multiplexer responsive to designation by the controller, an analog board for receiving electrical signals from a given battery cell and a control board for selectively initiating a load test, battery bank charging or voltage measurement.
While the battery monitoring system described in U.S. Pat. No. 5,923,148 A is capable of collecting and analyzing data from a plurality of battery cells within a battery bank, it is generally geared at testing batteries in industrial plants. Its applicability to battery modules in electric drive systems for vehicles is therefore limited. In particular, U.S. Pat. No. 5,923,148 A contains no information on how parameters obtained from the single cell measurements may be used for assessing and controlling the performance of the overall battery block.